In the world tour finals, Novak Djokovic is the defending champion at the event -- in fact the Serb has claimed it the last four years. And a fifth straight title would also help Djoker reclaim the world number one ranking from Andy Murray. But Nole, would get a stern test from Dominic Thiem in his opening group match. 

The Austrian would push the Serb to a tiebreak in the opening set -- and he would be on point, getting the backhand winner, which prompts a smile from Djoker.

Thiem would win a marathon opening extra session, taking it 12-10 thanks to this wicked forehand winner.

But that would be it for him, as he came unglued in the second set, Djoker getting a break in the opening game.

Djokovic would not drop a game in the frame and was in complete control.

And the world number two would cruise in the decider, getting the service winner to seal a 6-7, 6-0, 6-2 win.

RAONIC TOPS MONFILS 6-3, 6-4

Also in the Ivan Lendl group was Milos Raonic at the bottom of your screen serving to Gael Monfils, the Canadian comes to the net, when the Frenchman decides to go between his legs with the return, but Raonic takes the point en route to winning the set 6-3.

Off to the second, on serve in the seventh game, and the two wage in a decent rally, but the Canadian who is dealing with a thigh problem, seems to be moving around the court ok, and takes this point with a lovely backhand, and breaks his opponent.

Raonic would then serve things out and gets the service winner on match point to seal a 6-3, 6-4 win and meets Djoker in his next match.